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Sir Joseph John Thomson
(1856 - 1940)
English physicist who helped revolutionize the knowledge of atomic structure
by his discovery of the electron (1897). He received the Nobel Prize
for Physics in 1906 and was knighted in 1908.
Education and early career.
Thomson was the son of a bookseller in a suburb of Manchester. When
he was only 14, he entered Owens College, now the Victoria University
of Manchester. He was fortunate in that, in contrast with most colleges
at the time, Owens provided some courses in experimental physics. In
1876 he obtained a scholarship at Trinity College, Cambridge, where
he remained for the rest of his life. After taking his B.A. degree in
mathematics in 1880, the opportunity of doing experimental research
drew him to the Cavendish Laboratory. He began also to develop the theory
of electromagnetism. As set forth by James Clerk Maxwell, electricity
and magnetism were interrelated; quantitative changes in one produced
corresponding changes in the other.
Prompt recognition of Thomson's achievement by the scientific community
came in 1884, with his election as a fellow of the Royal Society of
London and appointment to the chair of physics at the Cavendish Laboratory.
Thomson entered physics at a critical point in its history. Following
the great discoveries of the 19th century in electricity, magnetism,
and thermodynamics, many physicists in the 1880s were saying that their
science was coming to an end like an exhausted mine. By 1900, however,
only elderly conservatives held this view, and by 1914 a new physics
was in existence, which raised, indeed, more questions than it could
answer. The new physics was wildly exciting to those who, lucky enough
to be engaged in it, saw its boundless possibilities. Probably not more
than a half dozen great physicists were associated with this change.
Although not everyone would have listed the same names, the majority
of those qualified to judge would have included Thomson.
Discovery of the electron.
Thomson's most important line of work, interrupted only for lectures
at Princeton University in 1896, was that which led him, in 1897, to
the conclusion that all matter, whatever its source, contains particles
of the same kind that are much less massive than the atoms of which
they form a part. They are now called electrons, although he originally
called them corpuscles. His discovery was the result of an attempt to
solve a long-standing controversy regarding the nature of cathode rays,
which occur when an electric current is driven through a vessel from
which most of the air or other gas has been pumped out. Nearly all German
physicists of the time held that these visible rays were produced by
occurrence in the ether--a weightless substance then thought to pervade
all space--but that they were neither ordinary light nor the recently
discovered X rays. British and French physicists, on the other hand,
believed that these rays were electrified particles. By applying an
improved vacuum technique, Thomson was able to put forward a convincing
argument that these rays were composed of particles. Furthermore, these
rays seemed to be composed of the same particles, or corpuscles, regardless
of what kind of gas carried the electric discharge or what kinds of
metals were used as conductors. Thomson's conclusion that the corpuscles
were present in all kinds of matter was strengthened during the next
three years, when he found that corpuscles with the same properties
could be produced in other ways--e.g., from hot metals. Thomson may
be described as "the man who split the atom" for the first
time, although "chipped" might be a better word, in view of
the size and number of electrons. Although some atoms contain many electrons
their total mass is never so much as 1/1000 that of the atom.
By the turn of the century most of the scientific world had fully accepted
Thomson's far-reaching discovery. In 1903 he had the opportunity to
amplify his views on the behaviour of subatomic particles in natural
phenomena when, in his Silliman Lectures at Yale, he suggested a discontinuous
theory of light; his hypothesis foreshadowed Einstein's later theory
of photons. In 1906 he received the Nobel Prize for Physics for his
researches into the electrical conductivity of gases; in 1908 he was
knighted; in 1909 he was made president of the British Association for
the Advancement of Science; and in 1912 he received the Order of Merit.
Thomson was, however, by no means a scientific recluse. During his
most fruitful years as a scientist, he was administrative head of the
highly successful Cavendish Laboratory. (It was there that he met Rose
Elizabeth Paget, whom he married in 1890.) He not only administered
the research projects but also financed two additions to the laboratory
buildings primarily from students' fees, with little support from the
university and colleges. Except for its share of a small government
grant to the Royal Society to aid all British universities and all branches
of science, the Cavendish Laboratory received no other government subsidy,
nor were there contributions from charitable corporations or industry.
A gift from a devoted staff member made possible the purchase of a small
liquid-air machine essential for Thomson's research on positive rays,
which greatly increased knowledge of the recently discovered atomic
nuclei.
Thomson was, moreover, an outstanding teacher; his importance in physics
depended almost as much on the work he inspired in others as on that
which he did himself. The group of men he gathered around him between
1895 and 1914 came from all over the world, and after working under
him many accepted professorships abroad. Seven Nobel Prizes were awarded
to those who worked under him. Thomson took his teaching duties very
seriously: he lectured regularly to elementary classes in the morning
and to postgraduates in the afternoon. He considered teaching to be
helpful for a researcher, since it required him to reconsider basic
ideas that otherwise might have been taken for granted. He never advised
a man entering a new research field to begin by reading the work already
done. Rather, Thomson thought it wise that he first clarify his own
ideas. Then he could safely read the reports of others without having
his own views influenced by assumptions that he might find difficult
to throw off.
Thomson demonstrated his wide range of interests outside science by
his interest in politics, current fiction, drama, university sports,
and the nontechnical aspects of science. Although he was not athletic,
he was an enthusiastic fan of the Cambridge cricket and rugby teams.
But his greatest interest outside physics was in plants. He enjoyed
long walks in the countryside, especially in hilly regions near Cambridge,
where he searched for rare botanical specimens for his elaborate garden.
In 1918 Thomson was made master of Trinity College. This position, in
which he remained until his death, gave him the opportunity to meet
many young men whose interests lay outside the field of science. He
enjoyed these meetings and made many new friends.
Assessment.
To a large extent, it was Thomson who made atomic physics a modern science.
The studies of nuclear organization that continue even to this day and
the further identification of elementary particles all followed his
most outstanding accomplishment, his discovery of the electron in 1897.
Although this new physics has continued to raise more theoretical questions
than can be answered at present, from the start it rapidly gave rise
to practical applications in technology and industry.
BIBLIOGRAPHY.
J.J. Thomson and G.P. Thomson, Conduction of Electricity Through Gases,
3rd ed., 2 vol. (1928-33, reprinted 1969); and J.J. Thomson, Recollections
and Reflections (1936, reprinted 1975), are representative of Thomson's
work. His life and career are traced in Lord Rayleigh, The Life of Sir
J.J. Thomson, O.M. (1942, reprinted 1969); and G.P. Thomson, J.J. Thomson
and the Cavendish Laboratory in His Day (1964; also published as J.J.
Thomson: Discoverer of the Electron, 1966).
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